This invention relates to a novel glass support rod or "bead" as it is referred to in the art. Beads of this character are support components of electron-gun mount assemblies for cathode-ray tubes and other types of vacuum electron tubes.
A cathode-ray tube, such as a color television picture tube, comprises an evacuated envelope having a target and an electron-gun mount assembly supported therein. During the operation of the tube, the mount assembly produces one or more electron beams for selectively scanning the target for its designated purpose. The mount assembly comprises two or more glass support rods or beads from which various electrodes are supported to form a coherent unit as is commonly known in the art.
The beads are prepared by pressing powdered glass and a binder in a mold to produce bodies of a desired shape, and then sintering the bodies to remove the binder from the bodies, to develop strength in the bodies and to seal the pores of the bodies. The bodies are generally rectangular with flat ends and may be any size. One common size is about 48 mm (millimeters) by 11 mm by 4.37 mm thick. The corners are quite sharp, having almost no radius when pressed and up to about 0.1 mm (4 mils) of thermally-induced radius after sintering.
Prior to assembling into mount assemblies, the beads are washed to remove residual binder and mold release compound. Then, if desired, portions of the surface may be metalized or otherwise treated. During this processing, prior beads have a tendency to break or chip at the corners thereof, particularly the corners at the ends of the beads. As many as 20% of the beads in a batch have been rejected for breakage or chipping. Because the beads are electrically insulating, they attract and hold glass and other electrically insulating particles electrostatically, which particles are then difficult to remove. But, since they may later be released and may interfere with the operation of the tube, they must be removed or, better still, never be generated.